To avoid the problem of pipes and/or material intended to flow therein freezing or such material becoming undesirably viscous in cold temperatures, heat trace cable has been used to warm the pipes and the material therein. An exemplary heat trace cable is comprised, inter alia, of a pair of conductors that extend in parallel along the length of the cable, heat producing electrical resistance material between the conductors, and an electrical insulation material covering the conductors and the resistance material. Typically at one end of such heat trace cable the conductors are connected to a source of electrical power, such as available line power of, say, 120 volts, 60 Hz. In response to energization by such an electrical source the heat trace cable produces a heat output that may be used to warm a pipe along which it is placed or about which it is wrapped, for example. Heat trace material also may be used to warm large holding or storage tanks. Preferably the heat trace cable is in direct engagement with the external surface of the pipe or tank for maximum thermal transfer efficiency with respect thereto. Moreover, thermal insulation usually over the pipe or tank and heat trace cable helps to retain the heat developed by the cable and to exclude external cold from the pipe and material flowing therein. A further weather resistant layer of protective material also may protect the thermal insulation and the underlying pipe and heat trace cable from moisture, e.g. rain or snow, and from other harsh or caustic chemicals or other pollutants in the local environment.
A problem that may be encountered when heat trace cable is used as above, for example, is that a failure may occur in the heat trace cable whereby a length thereof may be deenergized or otherwise damaged so as not to produce the needed heating of the pipe and material therein. As a result of such lack of heat the pipe may become damaged and leak, and other problems also may occur, for example to the immediate fluid system or to apparatus upstream or downstream of the unheated area, to the fluid itself, etc.
Often such heat trace cable protected pipelines are one hundred feet or even several hundred feet in length, and they may be mounted high above ground for safety, clearance and/or other reasons. Fluid leaking from such a damaged pipe may travel along the insulation material and external protective layer of material before becoming visible to a service or maintenance person and, therefore, may not be a good indicator of the actual location of the damaged part of the pipeline. Accordingly, to locate such damaged portion may be a very difficult and time consuming task, for example requiring the service or maintenance person working in a relatively precarious location to remove a substantial length of protective and insulation material to find the damage.
In the past to help prevent such damage to such pipes or pipelines (pipe and pipeline being used interchangeably herein and generically to represent devices with which heat trace or like material would be used), beginning and ending indicator assemblies have been connected to the heat trace cable at the power input end and at the opposite end thereof to indicate that power was being input to heat trace cable and that power was reaching the opposite end of the heat trace cable remote from the power input end thereof, respectively. If either such indicator assembly were not showing light, an effort could be made to stop the pipe flow before damage occurred. Such prior indicator assemblies required heavy metal boxes to withstand the harsh environments, such as water and other severe weather conditions, harsh chemical pollutants, etc., and to protect the actual indicators themselves, such as electric lamps. Also, such indicator assemblies are relatively expensive to purchase and because of the size and weight thereof are rather difficult to install; usually they would have to be installed in a certain upright condition to assure watertight condition thereof. Additionally, such indicator assemblies have been difficult to service due to frequently encountered damage to the boxes thereof from the harsh environment in which they are located and possibly also due to the relatively inaccessible locations thereof.
Furthermore, if the remote end indicator assembly were not showing light when the beginning indicator was showing light (indicating power input to the heat trace cable but failure of power to reach the remote end of the cable), there was no way to determine the location of the actual failure without inspecting the length of the pipeline until such failure location were found. The time and cost to make such an inspection, including removal of substantial lengths of insulation and weatherproofing material, as well as the potential hazzard involved, especially when the maintenance person is working high above ground, can be substantial.